Aluminum extruded shapes are articles that are extrusion-molded from a material such as aluminum or aluminum alloy by an extruding machine and are widely used, for example, in doors and windows.
The aluminum extruded shapes may have external defects occurring on the surfaces thereof. Depending on the degree of an external defect, the aluminum extruded shape cannot be used as a product due to its inferior surface condition. This give rise to a need for an inspection performed to determine as to whether an aluminum extruded shape has on its surface such an external defect as to render the aluminum extruded shape unusable and reject the aluminum extruded shape with such external defect as a defective article.
Conventionally, through visual inspection by a human operator, surface conditions of an aluminum extruded shape are checked for external defects that may occur on a surface of the aluminum extruded shape. If the inspected surface conditions of the aluminum extruded shape are determined to be unusable as a product due to external defects, the inspected aluminum extruded shape is rejected as a defective article.
However, the visual inspection by the human operator is insufficient in terms of reliability due to variations in skills in judging defective articles such that the judgment given to reject a defective article to be unusable as a product varies with the level of skill of the human operator and the inspection results depend on individual human operators.
With the difficulties in view, a visual inspection apparatus computerized to perform a visual inspection of aluminum extruded shapes is disclosed, for example, in Japanese Patent Laid-open Publication (JP-A) No. 2004-061311.
The disclosed visual inspection apparatus for aluminum extruded shapes is configured to take an image of the surface of an aluminum extruded shape by a camera immediately after the aluminum extruded shape is extrusion-molded from an extruding machine, detect the degree of a surface defect through image processing of the picked up image, and make a judgment about whether the inspected aluminum shape is to be an defective article depending on the degree of the surface defect.
Specifically, an image picked up from the surface of an aluminum extruded shape is divided into small areas each having predetermined widths in a main scanning direction perpendicular or normal to an extruding direction and an auxiliary scanning direction parallel to the extruding direction, respectively. At least two of the small areas are compared for their average shades, and an absolute value of the difference between maximum and minimum average shades is stored. Then the absolute value of the shade difference is compared with a reference value and if it is not less than the reference value, a judgment to reject a defective article is rendered.
The above-described conventional visual inspection apparatus is particularly effective for the inspection of so-called “streaks”, that is, band-like patterns with different color tones along the extruding direction.
However, the external defects occurring on the surfaces of aluminum extruded shapes may include other external defects than the streaks.
For example, such external defects as so-called “dice marks” are “rough surfaces” may occur too.
The quality of surface conditions influenced by external defects such as dice marks, rough surfaces, and streaks can be detected through the afore-mentioned visual inspection performed by human operators. However, in the conventional external inspection apparatus, the quality of surface conditions involving a surface defect in the form of a dice mark, a rough surface cannot be occasionally detected.
Furthermore, the judgment of non-defective/defective articles based on the comparison of a shade difference obtained through image processing with a reference value, as done in the conventional visual inspection apparatus, cannot always secure reliable selection between non-defective articles and defective articles. For instance, judgments of non-defective/defective articles passed through the image processing may occasionally disagree with judgments of non-defective/defective articles made by human operators through visual inspection. Thus, it may occur that the articles, which were judged to be non-defective by the visual inspection apparatus, are judged to be defective at the visual inspection by the human operator, or alternatively, the articles that were judged to be defective by the visual inspection apparatus are judged to be non-defective at the visual inspection by the human operator.
It is accordingly an object of the present invention to provide a visual inspection apparatus, which can surely distinguish non-defective articles from defective articles, and is capable of detecting the quality of surface conditions based on external defects, such as streaks, dice marks and rough surfaces, occurring on the surface of an aluminum extruded shape to thereby ensure that an aluminum extruded shape having surface conditions so inferior as to render the aluminum extruded shape unusable as a product can be rejected as an defective article.